This research seeks to investigate in greater depth the function of two alternative sigma factors of M. tuberculosis, SigL and SigM, which have been the focus of recent study in the PI's laboratory. Data from the PI's laboratory indicate that these sigma factors regulate genes involved in surface lipid and secreted protein synthesis. These two sigma factors appear to play distinct roles in regulating different aspects of surface lipid biosynthesis in M. tuberculosis. SigM negatively regulates several lipid biosynthetic pathways that have been shown to be important for early stages of M. tuberculosis infection. In contrast, SigL, which is critical for the virulence of this organism, positively regulates two polyketide synthase genes, pks7 and pks10, that also have been implicated in virulence. In addition to their role in regulating lipid biosynthesis, both of these sigma factors regulate genes encoding secreted proteins. SigL regulates the gene for the major secreted protein antigen Mpt53, while SigM is required for the expression of two pairs of ESAT-6-like secreted proteins. The hypothesis underlying this research is that these sigma factors and the genes they regulate play key roles in the modulation of the interaction between M. tuberculosis and the host during the course of infection, via regulation of genes for surface lipid and secreted protein production. The overall goal of this proposal is thus to investigate the function of these two sigma factors by characterizing the regulation and function of these lipids and secreted proteins, and their role in host-pathogen interactions. [unreadable] [unreadable] This goal will be achieved through four specific aims. Aim 1 will characterize the role of SigL in regulating specific lipid biosynthesis, and the role of these lipids in virulence. Aim 2 will determine the function of the SigL-regulated major secreted protein antigen Mpt53 and its role in virulence. Aim 3 will characterize the role of SigM in regulating secreted protein and lipid biosynthesis. Aim 4 will investigate the role of SigM in M. tuberculosis pathogenesis and characterize the cellular immune response to the SigM-regulated secreted proteins EsxE, EsxF, EsxT and EsxU. [unreadable] [unreadable] Health Significance: Tuberculosis remains a major human pathogen worldwide and in the United States, and treatment requires prolonged multi-drug therapy. The insights achieved by this research into M. tuberculosis pathogenesis and the host responses to this pathogen may identify new approaches to developing more effective treatment for this infection. [unreadable] [unreadable] [unreadable]